arXiv subjects

Ashim Sen Gupta

Publications and source records attributed to Ashim Sen Gupta.

3 recordsLinked to original sources

arXiv2024

K-mouflage at high $k$: extending the reach of $\texttt{Hi-COLA}$

The $\texttt{Hi-COLA}$ code is an efficient dark matter simulation suite that flexibly handles the Horndeski family of modified gravity models. In this work we extend the scope of $\texttt{Hi-COLA}$ to accommodate Horndeski theories with K-mouflage screening, allowing for the computation of matter power spectra in the non-linear regime in these models. We explore the boost of the dark matter power spectrum relative to GR-$\Lambda$CDM in K-mouflage gravity, and also discuss how large-scale structure computations change between the Einstein and Jordan frames. A dissection of the relative contributions of the modified background, linear growth, fifth force, and the conformal factor (a new inclusion to $\texttt{Hi-COLA}$) to the boost factor is presented. The ability of $\texttt{Hi-COLA}$ to run with general Horndeski models and multiple screening mechanisms makes it an ideal tool for testing gravity with upcoming galaxy survey data.

astro-ph.CO↗

arXiv2024

Matter Power Spectra in Modified Gravity: A Comparative Study of Approximations and $N$-Body Simulations

Testing gravity and the concordance model of cosmology, $Λ$CDM, at large scales is a key goal of this decade's largest galaxy surveys. Here we present a comparative study of dark matter power spectrum predictions from different numerical codes in the context of three popular theories of gravity that induce scale-independent modifications to the linear growth of structure: nDGP, Cubic Galileon and K-mouflage. In particular, we compare the predictions from full $N$-body simulations, two $N$-body codes with approximate time integration schemes, a parametrised modified $N$-body implementation and the analytic halo model reaction approach. We find the modification to the $Λ$CDM spectrum is in $2\%$ agreement for $z\leq1$ and $k\leq 1~h/{\rm Mpc}$ over all gravitational models and codes, in accordance with many previous studies, indicating these modelling approaches are robust enough to be used in forthcoming survey analyses under appropriate scale cuts. We further make public the new code implementations presented, specifically the halo model reaction K-mouflage implementation and the relativistic Cubic Galileon implementation.

astro-ph.CO↗

arXiv2023

$\texttt{Hi-COLA}$: Fast, approximate simulations of structure formation in Horndeski gravity

We introduce $\texttt{Hi-COLA}$, a code designed to run fast, approximate $\textit{N}$-body simulations of non-linear structure formation in reduced Horndeski gravity. Given an input Lagrangian, $\texttt{Hi-COLA}$ dynamically constructs the appropriate field equations and consistently solves for the cosmological background, linear growth, and screened fifth force of that theory. Hence $\texttt{Hi-COLA}$ is a general, adaptable, and useful tool that allows the mildly non-linear regime of many Horndeski theories to be investigated for the first time, at low computational cost. In this work, we first describe the screening approximations and simulation setup of $\texttt{Hi-COLA}$ for theories with Vainshtein screening. We validate the code against traditional $\textit{N}$-body simulations for cubic Galileon gravity, finding $2.5\%$ agreement up to $k_{\rm max}=1.2~h/{\rm Mpc}$. To demonstrate the flexibility of $\texttt{Hi-COLA}$, we additionally run the first simulations of an extended shift-symmetric gravity theory. We use the consistency and modularity of $\texttt{Hi-COLA}$ to dissect how the modified background, linear growth, and screened fifth force all contribute to departures from $Λ$CDM in the non-linear matter power spectrum. $\texttt{Hi-COLA}$ can be found at https://github.com/Hi-COLACode/Hi-COLA .

astro-ph.CO↗